Power and free conveyor system with variable length carriers

ABSTRACT

A conveyor system for track supported carriers, each having a driving dog engageable by a pusher, in which each carrier has front and rear trolleys connected by front and rear tow bar members that are relatively movable longitudinally of the track to extend or reduce the length of the carrier. A latch device provides a plurality of selectable relative positions of the tow bar members and a latch release mounted adjacent the carrier track permits the carrier length to be changed as desired. The length of a carrier may be changed by installing the latch release on an inclined section of track; or the carrier length may be adjusted as desired by stopping one of the carrier trolleys, releasing the latch device, and moving the other trolley by an auxiliary pushing apparatus.

United States Patent Macomber et al.

Inventors: Robert A. Macomber, Novi; Clarence A. Dehne, Farmington, both of Mich.

Assignee: Jervis B. Webb Company Filed: Aug. 19, 1970 Appl. N0.: 64,975

us. 01 ..104/89, 104 172 s Int. Cl. ..B6lb 3/00 Field of Search ..104/172 5, 17s, 89, 96;

105/393; 280/34 T; 287/58 CF References Cited UNITED STATES PATENTS 4/ l 967 Potter et al. 104/96 3/ l 960 Romans 105/89 9/1957 Atkins ..287/58 CT 2/1949 Stark, Jr ..280/34 T 15 3,683,817 1- Aug. 15, 19 72 Assistant Exdminer-Robert Saifer AttorneyFarley, Forster & Farley 5 7] ABSTRACT A conveyor system for track supported carriers, each having a driving dog engageable by a pusher, in which each carrier has front and rear trolleys connected by front and rear tow bar members that are relatively movable longitudinally of the track to extend or reduce the length of the carrier. A latch device provides a plurality of selectable relative positions of the tow bar members and a latch release mounted adjacent the carrier track permits the carrier length to be changed as desired, The length of a carrier may be changed by installing the latch release on an inclined section of track; or the carrier length may be adjusted as desired by stopping one of the carrier trolleys, releasing the latch device, and moving the other tr0lley by an auxiliary pushing apparatus.

26 Claims, 12 Drawing Figures Mummwm mz 3.683.817

SHEET 2 OF 6 ATTORNEYS PATENTEUAUGISIQIZ sum surg INVENTORS FOfiZKT/I. MHfO/MBZR (Z Y ATTORNEYS PATENTED Ana 1 5 I972 SHEET 8 OF 6 ATTORNEYS POWER AND FREE CONVEYOR SYSTEM WITH VARIABLE LENGTH CARRIERS SUMMARY OF THE INVENTION This invention relates to improvements in a conveyor system of the type having carriers supported on a carrier track and driven by engagement of driving dogs on the carriers by pushers of a separately supported propelling member. The improvements of the invention permit the length of a carrier to be automatically extended or reduced as desired, thereby enabling the handling of a variety of different length loads in a single system and enabling the carrier length to be changed according to load conditions. For example, in a system where. carriers circulate between a loading station and an unloading station, unloaded carriers being returned for loading can be reduced in length to conserve space and then each extended in length as required to match the next load.

In the conveyor system of the invention, a carrier has at least one front and one rear trolley interconnected by a tow or load bar which comprises a front member connected to the front trolley and extending toward the rear trolley, and a rear member connected to the rear trolley and extending toward the front trolley. These tow bar members are supported one upon the other for relative longitudinal movement so that the length of the carrier can be extended and reduced. A latch device releasably connects the tow bar members together in one of a plurality of selectable relative positions.

This latch device is releasable by means mounted adjacent the carrier supported track, and a change in the length of a carrier can be obtained either by installing the latch releasing means on an inclined section of the carrier supporting track, or by employing in combination with the latch releasing means an auxiliary pushing mechanism capable of engaging and moving one part of the carrier relative to' another part thereof to produce relative longitudinal movement between the tow bar members. In the preferred embodiment disclosed herein, the carrier driving dog is mounted on a driving trolley located rearwardly of the front carrier trolley, and latch releasing means are installed on an upwardly inclined section of the carrier track following an unloading station with the result that all carriers passing this latch releasing means are automatically reduced to a minimum length for return to a loading station. In advance of the loading station, means are provided for adjusting the length of the carrier as desired, and consist of the combination of a stop which arrests forward movement of the driving trolley and rear tow bar member, a latch releasing means, and auxiliary pusher apparatus which engages and moves the forward trolley and load bar a desired distance relative to the rear trolley and load bar.

Preferably, the latch device consists of a latch member carried by one of the tow bar members and having a latch portion engageable with one of a plurality of detents spaced longitudinally along the other tow bar member, and a latch retainer capable of engaging and holding the latch member in both the locking and released positions of the latter. The latch and latch retainer members are operable by cams mounted adjacent to the carrier track.

Other features and advantages of the invention will appear from the description to follow of the representa- '2 tive embodiment thereof disclosed in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is aside elevation showing a conveyor and carrier constructed in accordance with the invention;

FIG. 2 is an enlarged sectional elevation taken as indicated by the line 2-2 of FIG. 1 and including a latch device on the carrier and latch releasing means mounted adjacent to the path of carrier travel;

FIG. 3 is an enlarged elevation of the front portion of the carrier of FIG. 1

FIG. 4 is a sectional plan view taken as indicated by the line 4-4 of FIG. 3 and including a fragmentary showing of apparatus for changing the length of the carrier;

FIG. 5 is an enlarged elevation of the tow bar portion of the carrier of FIG. 1;

FIG. 6 is an enlarged sectional detail taken on the line 6--6 of FIG. 5;

FIG. 7 is an enlarged sectional detail taken on the line 7-7 of FIG. 5;

FIG. 8 is an enlarged sectional detail of the latch device and releasing means of FIG. 2, taken as indicated by the line 8-8 of FIG. 5.;

FIG. 9 is a detailed elevation of a releasing means of FIG. 2';

FIG. 10 is a plan view of the structure shown in FIG.

FIG. 12 is a schematic plan view illustrating carrier 1 length reducing and extending operations.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 1-4, the type of conveyor system to which the improvements of the invention relate includes an upper power track 10 for trolleys 12 which are connected to an endless propelling member or chain 13, driven by conventional driving means, not shown. Mounted below the power track 10, by hangars 14, is a carrier supporting track 16 formed by a pair of channel section members 17. A carrier 18 supported on the track 16 includes a driving trolley 20 having a holdback dog 23 and a driving dog 21 engageable by a pusher 22 secured to either the propelling chain 13 or to one of the chain supporting trolleys 12, as shown in FIG. 1. The driving trolley 20 may be of the type disdog 21 is moveable between driving and non-driving positions relative to a pusher 22, so that carriers may be stopped as desired throughout the system. A construction for a carrier stop for use with a driving trolley of this type is disclosed in U.S. 991 Pat. No. 3,229,645.

The carrier 18 illustrated is designed to handle a relatively long, heavy load 24, such as a vehicle chassis, and includes a front trolley assembly 26 and a rear trolley assembly 27. Each of these assemblies have a pair of load supporting trolleys 28, and the driving trolley 20 is connected to the rear trolley assembly 27 by a towing link 30. This arrangement of trolleys is illustrative only. With regard to the front and rear trolley assemblies 26 and 27, these could each consist of merely a single trolley under lighter load requirements, and, with respect to the driving trolley 20, in many cases it will also function as a load carrying trolley and will usually be located at the leading end of the carrier. Certain advantages to be described hereinafter, are obtainable in the present invention when the driving trolley 20 and the driving dog 21 are associated with the rear trolley or trolley assembly 27 of the carrier, but it is considered within the scope of the invention to employ a driving trolley as a forward load carrying trolley of the carrier or as a propelling unit connected to such a forward load carrying trolley. 7

With respect to trolleys, then, the essential elements of a carrier for use in a conveyor system according to the invention include at least one front trolley, one rear trolley and a driving dog associated with either of these trolleys.

FIGS. 2-4 show the construction of the front trolley assembly 26, which is substantially duplicated for the rear trolley assembly 27. A shaft 32 having a collar 33 adjacent the lower end thereof is connected to the body of each of the pair of trolleys 28 by a horizontal pivot pin 34, and a sleeve 35 is rotatably mounted on each shaft 32, a thrust bearing 36 being employed between the collar 33 and sleeve 35. A pair of longitudinally extending load beams 37 are connected to the pair of sleeves 35, as best shown in FIG. 4, and to a central load supporting sleeve 38. The sleeve 38 rotatably supports a vertical shaft 40 which is secured to a pair of transversely extending load bars 42 and is connected to a hangar 44 by a transverse pivot 45. A collar 46 fastened to the bars 42 engages a bearing 47 at the upper end of the sleeve 38. Load carrying attachments or hooks 50 are each secured by a chain 51 to a bracket 52 mounted on the bars 42.

The front and rear trolley assemblies 26 and 27 are interconnected by a tow bar 54 composed of a front tubular member 55 which is connected to the hangar 44 of the front trolley assembly 26 and extends toward the rear trolley assembly, and a rear tubular member 56 of larger diameter which is connected to the hangar 44 of the rear trolley assembly 27 and extends toward the front trolley assembly.

Details of the construction of the tow bar 54 are shown in FIGS. -7. The front tow bar member 55 and rear tow bar member 56 are supported one upon the other for relative longitudinal telescoping movement by means which include a circumferentially spaced cluster of rollers 58, shown in FIG. 6, each mounted on a bracket 59 carried by the rear and outer tow bar member 56 and engaging the surface of the front and inner tow bar member 55; and a second set of rollers 60, shown in FIG. 7, mounted on the end of the front tow bar member 55 and engaging the internal surface of the rear tow bar member 56. The roller set 60 consists of a bracket member 61 mounting a roller 62 and a roller 63 on an axis normal to the axis of the roller 62.

TI-Ie tow bar members 55 and 56 are releasably connected together in one of a plurality of selectable positions by a latch device 66, best shown in FIGS. 2 and 8. This latch device includes a latch member 67 having a locking portion 68 projecting through an aperture 69 in the tow bar member 56 and engageable in one of a plurality of detents 70 provided at suitable intervals on the front tow bar member 55; and, a latch retaining member 71 having a latch 72 engageable in a notch 73 or 74 in the latch member 67. A pair of parallel plates 76 and 77 (FIG. 5) are secured to the outer tow bar member 56 and fonn a bracket to which the latch member 67 is secured by a pivot 78 and the retaining member 71 by a pivot 79. The latch member 67 includes a laterally extending arm portion 80 carrying a roller follower 81, and this arm portion 80 with relation to the latch member pivot 78 acts as a counterweight normally biasing the latch member 67 to the full line position shown in FIG. 2 and FIG. 8 in which the locking portion 68 engages a detent 70 on the tow bar member 55. The retaining member 71 also includes a laterally extending arm 82 equipped with a roller follower 83, but the portion 84 of the retaining member, on the side of the pivot 79 opposite the arm 82, is formed with sufficient mass to act as a counterweight, overcoming the mass of the arm 82 and biasing the retaining member to a position in which the latch 72 on the retaining member engages one of the notches 73 or 74 in the latch member 67. In the full line or locked position of the members shown in FIGS. 2 and 8, the latch 72 of the retaining member engages the notch 73 of the latch member and locks the latch member in this position.

Means for releasing the latch device are mounted adjacent the carrier supporting track members 17 atany desired location in the conveyor system, and are illustrated in FIGS. 2 and 8-10. The releasing means includes a cam 86 shown at the left side of FIGS. 2 and 8 capable of moving the latch member 67 from the locked position shown in full line toward a released position, as shown in broken line in FIG. 8, and a cam 88 at the right hand side of FIGS. 2 and 8, capable of moving the retaining member 71 from the locked position shown in full line toward a released position as shown in broken line in FIG. 8.

FIGS. 9 and 10 illustrate the construction and mounting of the cam 88, consisting of suitable bracket structure 90 secured to one of the carrier track members 17; the cam 88, as shown in FIG. 10, including an actuating portion 91 extending angularly to the track 17 and a retaining portion 92 extending parallel thereto. The construction and mounting of the cam 86 are similar to the cam 88. However it will be understood that the retaining member cam 88 is positioned along the path of carrier travel in advance of the locking member cam 86 so that the retaining member 71 is moved to released position prior to the locking member 67. Also, the portion 92 of the retaining member cam 88 terminates prior to the corresponding portion of the locking member cam 86' so that the retaining member 71 is released from the cam 88 and the latch 72 falls into engagement with the notch 74 on the latch member 67, holding the latch member in released position. This relationship between the cams 86 and 88 is shown in FIG. 12 and will be further described.

FIGS. 11 and 12 illustrate representative features and advantages obtainable from the invention in a conveyor system. In FIG. 11, the load 24 is transferred from the carrier 18 of the overhead power and free conveyor, traveling in the direction indicated by the arrow 94, to a schematically illustrated flat top conveyor 95 moving in the same direction as indicated by the arrow 96.

Approaching the transfer zone, the tracks and 16 of the overhead conveyor are gradually inclined downwardly to a load transfer level indicated by the reference 97 at which the front end of the load 24 is supported on the conveyor 95 and the hooks 50 (FIG. 1) supporting the front end of the load can be manually disengaged therefrom. The rear end of the load is still suspended from the carrier 18 which is propelled at substantially the same speed as the conveyor 95 until the rear trolley assembly 27 of the carrier reaches the load transfer level 97 and the load is completely disengaged. Following the transfer level 97, the conveyor tracks 10 and 16 are inclined aburptly upwardly as indicated by the reference 98 to return the carrier to a clearance height. By propelling the carrier from the driving trolley 20 through the rear trolley assembly 27, the carrier can be cleared from the transfer area in less time and in less space. The front end of the carrier can commence moving to a clearance relation up the incline 98 (which changes the rate of movement relative to the conveyor 95) immediately after the load has been disconnected, while the load continues to be advanced by the rear trolley assembly 27 at a proper relative rate for transfer to the conveyor 95.

An empty carrier 18 traveling up the inclined section 98 may be immediately transferred to another power conveyor, indicated by the upper track 10, for return at a different rate of travel to a carrier storage or loading area.

Empty carriers may be automatically reduced to a minimum length by providing latch device releasing cams 86 and 88 along the upwardly inclined section 98, as shown. These releasing cams are arranged as schematically indicated at the right hand portion of FIG. 12. Cam 88 engaged by the latch releasing member 71 is located in advance of the cam 86 engaged by the latch member 67 with relation to the direction of travel 94. Consequently, the latch retaining member 71 first engages the cam 88 and is moved to a released position relative to the latch member 67 which then engages the cam 86 and is in turn moved to released position relative to a detent 70 on the carrier front tow bar 55. The latch retaining member 71 disengages from the cam 88 while the latch member 67 is still engaged with the cam 86, and hence the retaining member 71 returns from a full released position to a position in which the latch element 72 thereon engages the notch 74 on the latch member 67, and when the latch member 67 then disengages from the cam 86, the retaining member 71 holds the latch member in released position.

The combination of gravity and the forward motion of the rear trolley assembly 27 produces an inward telescoping relative movement between the tow bars 55 and 56 until the minimum carrier length is reached as defined by abutment between rear tow bar 56 and front hangar 44, or other suitable movement limiting means. The latch retaining member 71 then engages a second cam 88' shown in FIG. 12, the latch element 72 is moved out of engagement with the notch 74 on the latch member 67 which then returns to latched position, and the retaining member is then returned to locking position.

Essential elements of a carrier length adjusting station are schematically shown in the left hand portion of FIG. 12, and it will be assumed that each carrier, prior to arriving at this station, has been reduced to minimum length as just described. THese components include a carrier stop.l00 having a stop plate 101 capable of depressing the carrier driving dog 21 and being abutted by a hold back dog 23 on the driving trolley 20 as more fully described in U.S. Pat. NO. 3,229,645 3,229,645; a retaining member cam 88 and a latch member cam 86 selectively positionable by actuating cylinders 102 and 103; and, auxiliary pusher apparatus 104 consisting of a suitably driven propelling member 105 equipped with one or more one-way pushers 106.

If the length of a carrier is to be changed, the stop 100 is actuated, moving the stop plate 101 to blocking position as shown, and the driving trolley 20 of the carrier is stopped with the rear trolley assembly 27 and rear tow bar 56 in a position at which the latch is released by the cams 88 and 86 which also have been positioned to be engaged by the latch retaining member 71 and latch member 67 respectively. In this position of the carrier, the transverse load bars 42 on the front trolley assembly 26 can be engaged by a pusher 106, when the auxiliary pusher apparatus 104 is activated, to advance the front trolley assembly 26 and front load bar 55 the proper distance for the length of carrier desired. The actuating cylinders 102 and 103 are then energized to release the cams 86 and 88 and lock the carrier tow bars'55 and 56 together. The stop plate 101 is then retracted and the carrier is picked up by the next advancing pusher 22.

Operation of these various components of the length adjusting station are preferably. controlled automatically, as in response to the setting of the desired length for a carrier, by a system of control elements which has not been shown, as such a system is considered to be within the capability of those skilled in the control art.

What is claimed is:

1. In a conveyor system of the type having a carrier supporting track, a carrier including trolleys mounted on the carrier supporting track, a propelling member supported by an adjacent track and having a pusher en gageable with a main driving dog on the carrier, and the carrier having at least one front and one rear trolley interconnected by a tow bar; the improvement wherein the tow bar comprises a front member connected to the front trolley and extending toward the rear trolley, and a rear member connected to the rear trolley and extending toward the front trolley; means carried by at least one of the tow bar members engaging and supporting the other tow bar member for relative longitudinal movement between said members whereby the length of the carrier can be extended and reduced; and a latch device rcleasably connecting the tow bar members together in one of a plurality of selectable relative positions, the latch device including a remotely opera-' ble latch member.

2. A conveyor system according to claim 1 wherein means for releasing the latch device is mounted adjacent the carrier supporting track.

3. A conveyor system according to claim 2 wherein the carrier supporting track extends on an incline where the latch releasing means :is mounted whereby the length of the carrier is varied automatically is response to release of the latch device.

4. A conveyor system according to claim 3 further including means for limiting relative longitudinal movement between said tow bar members which occurs in response to release of the latch device.

5. A conveyor system according to claim 1 wherein the main driving dog on the carrier is mounted rearwardly of said front trolley.

6. A conveyor system according to claim 5 further including an upwardly inclined section in the carrier and propelling member supporting tracks, and means mounted adjacent the carrier supporting track for maintaining the latch device in released condition while at least said front carrier trolley is on the upwardly inclined section in the carrier supporting track whereby the length of the carrier can be reduced in response to release of the latch device.

7. A conveyor system according to claim 5 wherein the main driving dog on the carrier is provided on a driving trolley connected to said rear trolley.

8. A conveyor system according to claim 7 wherein the driving trolley is located between said front and rear trolleys.

9. A conveyor system according to claim 1 wherein said front and rear tow bar members are telescopingly arranged inner and outer tubes, said means carried by at least one of the tow bar members engaging and supporting the other tow bar member comprising inner rollers carried by the inner tube engaging the inner surface of the outer tube and outer rollers carried by the outer tube engaging the outer surface of the inner tube.

10. A conveyor system according to claim 9 wherein the latch member is movably mounted on the outer tube, a plurality of detents are spaced longitudinally along the inner tube, the latch member having a locking portion engageable with a selected detent.

11. A conveyor system according to claim 1 further including a carrier length adjusting station having means for releasing the latch device, and means for relatively moving the tow bar members to a desired carrier length.

12. A conveyor system according to claim 11 wherein the latch device comprises a plurality of longitudinally spaced detent elements provided on one of the tow bar members, the latch member being mounted on the other of the tow bar members for movement between a locking and a released position relative to a detent element, and said means for releasing the latch device includes actuating means for moving the latch member to released position.

13. A conveyor system according to claim 12 wherein the latch device includes means normally retaining the latch member in locking position, said means for releasing the latch device including actuating means for releasing the retaining means.

14. A conveyor system according to claim 1 further including a carrier length adjusting station comprising means for stopping one of said front and rear carrier trolleys, means for releasing the latch device, and apparatus mounted adjacent to the carrier supporting track for moving the other of said front and rear carrier trolleys to a desired carrier length.

15. A conveyor system according to claim 14 wherein the latch member, is movably mounted on the tow bar member connected to the stopped one of said front and rear carrier trolleys, and a plurality of detents are spaced longitudinally along the tow bar member connected to the other of said front and rear trolleys, the latch member having a locking portion engageable with a selected detent.

16. A conveyor system according to claim 1 wherein the latch device includes a plurality of longitudinally spaced detent elements provided on one of the tow bar members and the latch member is mounted on the other of the tow bar members for normally biased movement from a disengaged to an engaged position relative to a detent element; and retaining means for releasably holding the latch member in a disengaged position.

17. A conveyor system according to claim 16 further comprising means for actuating the latch device mounted adjacent to the carrier track and including means for moving the latch member to disengaged position and means for releasing the retaining means to permit movement of the latch member to engaged positron. I

18. A conveyor system according to claim 17 wherein the retaining means is capable of locking the latch member in engaged position, the means for actuating the latch device including means for unlocking the retaining means prior to moving the latch member to disengaged position.

19. A conveyor system according to claim 16 wherein the retaining means comprises a retaining member mounted on the other of the tow bar members for normally biased movement from a retaining to a locking position relative to the latch member, the retaining member in the locking and retaining positions being releasably engageable with the latch member in the engaged and disengaged positions, respectively.

20. A conveyor system according to claim 19 wherein the latch and retaining members each include a follower portion, and wherein latch and retaining member cam means are mounted adjacent the carrier supporting track for engagement by the respective follower portions to move the retaining member from locking position, move the latch member from engaged to disengaged position, move the retaining member to retaining position relative to the latch member and release the latch and retaining members for movement to engaged and locking position respectively.

21. A conveyor system according to claim 1 including a transfer station at which a load is removed from the carrier having the tow bar members in a relatively extended condition,

and means following the transfer station for reducing the length of the unloaded carrier including means for releasing the latch device.

22. A conveyor system according to claim 21 wherein the driving dog on the carrier is located so as to transmit driving force to a portion of the carrier other than and rearwardly of said front trolley, and the means following the transfer station for reducing the length of the unloaded carrier includes an upwardly inclined section in the carrier and propelling member supporting tracks, the means for releasing the latch device being operable to permit the carrier length to be reduced at least in part by gravitational force on the carrier produced by said upwardly inclined track sectlon.

23. A conveyor system according to claim 21 wherein the transfer station is one at which a load releasably supported by connections to forward and rearward portions of the carrier is deposited on a receiving conveyor, and the driving dog on the carrier is associated with the rearward portion of the carrier whereby the forward load connection can be released while the load is being advanced through the rearward load connection.

24. A conveyor system according to claim 23 wherein the driving dog on the carrier is provided on a driving trolley located between said front and rear trolleys and connected to the rear trolley.

25. A conveyor system according to claim 24 further including an upwardly inclined section in the carrier and propelling member tracks following the transfer .cludes cam means mounted adjacent the carrier track and engageable by follower means operatively associated with the latch device.

@ 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 683, 817 Dated August 15, 1972 Inventor(s) Robert Allen Macomber and Clarence A. Dehne It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 2, line 58, delete the numerals "99].";

Column 6, line 6, delete the numerals "3, 229, 645"; and,

Column 6, line 63, Change "is" second occurrence should read Signed and sealed this 6th day of March 1973- (SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. In a conveyor system of the type having a carrier supporting track, a carrier including trolleys mounted on the carrier supporting track, a propelling member supported by an adjacent track and having a pusher engageable with a main driving dog on the carriEr, and the carrier having at least one front and one rear trolley interconnected by a tow bar; the improvement wherein the tow bar comprises a front member connected to the front trolley and extending toward the rear trolley, and a rear member connected to the rear trolley and extending toward the front trolley; means carried by at least one of the tow bar members engaging and supporting the other tow bar member for relative longitudinal movement between said members whereby the length of the carrier can be extended and reduced; and a latch device releasably connecting the tow bar members together in one of a plurality of selectable relative positions, the latch device including a remotely operable latch member.
 2. A conveyor system according to claim 1 wherein means for releasing the latch device is mounted adjacent the carrier supporting track.
 3. A conveyor system according to claim 2 wherein the carrier supporting track extends on an incline where the latch releasing means is mounted whereby the length of the carrier is varied automatically is response to release of the latch device.
 4. A conveyor system according to claim 3 further including means for limiting relative longitudinal movement between said tow bar members which occurs in response to release of the latch device.
 5. A conveyor system according to claim 1 wherein the main driving dog on the carrier is mounted rearwardly of said front trolley.
 6. A conveyor system according to claim 5 further including an upwardly inclined section in the carrier and propelling member supporting tracks, and means mounted adjacent the carrier supporting track for maintaining the latch device in released condition while at least said front carrier trolley is on the upwardly inclined section in the carrier supporting track whereby the length of the carrier can be reduced in response to release of the latch device.
 7. A conveyor system according to claim 5 wherein the main driving dog on the carrier is provided on a driving trolley connected to said rear trolley.
 8. A conveyor system according to claim 7 wherein the driving trolley is located between said front and rear trolleys.
 9. A conveyor system according to claim 1 wherein said front and rear tow bar members are telescopingly arranged inner and outer tubes, said means carried by at least one of the tow bar members engaging and supporting the other tow bar member comprising inner rollers carried by the inner tube engaging the inner surface of the outer tube and outer rollers carried by the outer tube engaging the outer surface of the inner tube.
 10. A conveyor system according to claim 9 wherein the latch member is movably mounted on the outer tube, a plurality of detents are spaced longitudinally along the inner tube, the latch member having a locking portion engageable with a selected detent.
 11. A conveyor system according to claim 1 further including a carrier length adjusting station having means for releasing the latch device, and means for relatively moving the tow bar members to a desired carrier length.
 12. A conveyor system according to claim 11 wherein the latch device comprises a plurality of longitudinally spaced detent elements provided on one of the tow bar members, the latch member being mounted on the other of the tow bar members for movement between a locking and a released position relative to a detent element, and said means for releasing the latch device includes actuating means for moving the latch member to released position.
 13. A conveyor system according to claim 12 wherein the latch device includes means normally retaining the latch member in locking position, said means for releasing the latch device including actuating means for releasing the retaining means.
 14. A conveyor system according to claim 1 further including a carrier length adjusting station comprising means for stopping one of said front and rear carrier trolleys, means for releasing the latch device, and apparatus mounted adjacent to the carrier supporTing track for moving the other of said front and rear carrier trolleys to a desired carrier length.
 15. A conveyor system according to claim 14 wherein the latch member, is movably mounted on the tow bar member connected to the stopped one of said front and rear carrier trolleys, and a plurality of detents are spaced longitudinally along the tow bar member connected to the other of said front and rear trolleys, the latch member having a locking portion engageable with a selected detent.
 16. A conveyor system according to claim 1 wherein the latch device includes a plurality of longitudinally spaced detent elements provided on one of the tow bar members and the latch member is mounted on the other of the tow bar members for normally biased movement from a disengaged to an engaged position relative to a detent element; and retaining means for releasably holding the latch member in a disengaged position.
 17. A conveyor system according to claim 16 further comprising means for actuating the latch device mounted adjacent to the carrier track and including means for moving the latch member to disengaged position and means for releasing the retaining means to permit movement of the latch member to engaged position.
 18. A conveyor system according to claim 17 wherein the retaining means is capable of locking the latch member in engaged position, the means for actuating the latch device including means for unlocking the retaining means prior to moving the latch member to disengaged position.
 19. A conveyor system according to claim 16 wherein the retaining means comprises a retaining member mounted on the other of the tow bar members for normally biased movement from a retaining to a locking position relative to the latch member, the retaining member in the locking and retaining positions being releasably engageable with the latch member in the engaged and disengaged positions, respectively.
 20. A conveyor system according to claim 19 wherein the latch and retaining members each include a follower portion, and wherein latch and retaining member cam means are mounted adjacent the carrier supporting track for engagement by the respective follower portions to move the retaining member from locking position, move the latch member from engaged to disengaged position, move the retaining member to retaining position relative to the latch member and release the latch and retaining members for movement to engaged and locking position respectively.
 21. A conveyor system according to claim 1 including a transfer station at which a load is removed from the carrier having the tow bar members in a relatively extended condition, and means following the transfer station for reducing the length of the unloaded carrier including means for releasing the latch device.
 22. A conveyor system according to claim 21 wherein the driving dog on the carrier is located so as to transmit driving force to a portion of the carrier other than and rearwardly of said front trolley, and the means following the transfer station for reducing the length of the unloaded carrier includes an upwardly inclined section in the carrier and propelling member supporting tracks, the means for releasing the latch device being operable to permit the carrier length to be reduced at least in part by gravitational force on the carrier produced by said upwardly inclined track section.
 23. A conveyor system according to claim 21 wherein the transfer station is one at which a load releasably supported by connections to forward and rearward portions of the carrier is deposited on a receiving conveyor, and the driving dog on the carrier is associated with the rearward portion of the carrier whereby the forward load connection can be released while the load is being advanced through the rearward load connection.
 24. A conveyor system according to claim 23 wherein the driving dog on the carrier is provided on a driving trolley located between said front and rear trolleys and connected to the rear trolley.
 25. A Conveyor system according to claim 24 further including an upwardly inclined section in the carrier and propelling member tracks following the transfer station, and means for releasing the latch device so that the carrier length is reduced at least in part by upward movement of the front trolley on the inclined track section.
 26. A conveyor system according to claim 25 wherein the means for releasing the latch device includes cam means mounted adjacent the carrier track and engageable by follower means operatively associated with the latch device. 